Skeleton wheels and transfer cylinders are conventionally employed in printing presses for conveying freshly printed sheets from the impression cylinder of one printing station to the impression cylinder of a subsequent printing station. Sheets are often "marked" when the printed side of freshly printed surfaces contact surfaces of skeleton wheels and transfer cylinders.
A variety of 8 8 configurations and coverings have been proposed to reduce marking of sheets traveling through a printing press. The sheet transfer mechanism disclosed in U.S. Pat. No. 4,836,104 efficiently and effectively controls the path of the travel of a freshly printed sheet. However, in certain applications it is necessary to completely remove existing transfer cylinders and skeleton wheels for retro-fitting an existing printing press. A need persists for a suitable covering for existing skeleton wheels and transfer cylinders to prevent marking of sheets. U.S. Pat. No. 3,308,522 discloses an anti-offset roll having a ribbon of fabric having pile loops spirally wound about and secured to the surface of the cylinder.
U.S. Pat. No. 4,694,750 discloses a transfer cylinder having granular particles on the surface thereof in combination with elastic members having hooks on the end thereof adjustably secured around the circumference of the transfer cylinder and movable to positions longitudinally of the transfer cylinder most advantageous for the particular printing job.
U.S. Pat. No. 3,791,644 discloses a skeleton wheel for a printing press having an ink repellant, circumferential surface formed of polytetrafluoroethylene ("Teflon," a registered trademark). The first embodiment of the skeleton wheel is described as being wider than prior art thin-disc skeleton wheels having a plurality of very narrow, circumferentially spaced grooved projections for engaging a printed sheet. The first embodiment employed for example five skeleton wheels, each approximately four inches in width adjustable longitudinally of a delivery shaft to permit spacing of the wheels to engage the sheet in non-image areas. A second embodiment of the "Teflon" coated skeleton wheel is described as extending substantially the full width of the printing press.
U.S. Pat. No. 4,402,267 states that the "Teflon" coated wheel disclosed in U.S. Pat. No. 3,791,644, with continuous use over a period of time, experienced a slight accumulation of ink on the surface of the wheel. In an effort to overcome this problem, a layer of relatively loose-weave woven fabric gauze having a 40 count or 40 mesh was treated with a fabric softener commercially available under the trademark "DOWNEY" and with a fabric protector commercially available under the trademark "SCOTCH GUARD." The piece of fabric gauze is attached loosely around the surface of the skeleton wheel to permit and accommodate slight movement between the fabric and the surface of the skeleton wheel where the printed sheet is supported and conveyed by the skeleton wheel. However, when the fabric gauze picks-up and accumulates wet ink, it must be replaced since it cannot be cleaned or reconditioned while on the skeleton wheel.
U.S. Pat. No. 4,242,959 discloses a transfer drum provided with sheet carrying elements extending circumferentially around a transfer drum and spaced longitudinally of the drum, the sheet carrier elements being pivotable through 90.degree. into and out of a sheet engaging position.